It is known in the weaving loom art that the weft thread of a weaving loom can be guided through a thread preparation device in such a way that predetermined weft thread lengths can be accumulated by the device prior to their insertion into the shed of the loom. According to known embodiments, use is made of a weft storing device equipped with a drum, with an electromagnetically actuated pin mounted at the front end of the drum on its periphery. In this device, the weft thread is accumulated in coils on the drum, and a given number of coils of weft thread are released from the drum between sequential actuations of the pin that retract the pin from the drum periphery.
The drum surface is mainly composed of several such pins which are located at spaced intervals around the circumference of the drum and which are radially movable to extend from the drum surface and engage the weft thread in order to achieve a length adjustment of the weft thread length accumulated on the drum. The adjustments of the weft thread length must be carried out manually beforehand, prior to weft insertion. Quite obviously, this is a tedious job that renders automatic adjustment of the weft thread impossible.
It is also known to provide several thread locking elements along the periphery of the aforesaid drum, for example, the magnetically actuated pins, in such a way that less than a complete turn or coil of thread is released from the drum at each actuation of the electromagnetic pins.
Such a device has, however, the disadvantage that automatic adjustment can only achieve a step-wise length adjustment of the length of thread accumulated and that, consequently, in order to make a sufficient adjustment of the thread length, a small thread length in excess of what is needed for the adjustment is lost for each weft thread length accumulated. In this respect, it should not be forgotten that even a small thread excess for each weft thread length accumulated for insertion corresponds to a relatively large total weft thread loss for the woven fabric.